Transcript PPT - University of Nairobi

ERASTUS K. KANG’ETHE
UNIVERSITY OF NAIROBI
[email protected]
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 Is
made by bees from nectar from flowers
(Floral) and from tree saps (Honey dew).
 Man is indebted to the honeybee for
searching earths fields and forests for
their treasured sweetness
 Prepared by the bee from natural
solutions, changed from an easily spoiled
thin sweet liquid to a stable high density
energy food
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 Definition: Honey
is twice stolen sweet.
Stolen sweets are said to be the best.
Prov 9 :17
 Stolen once by the bees from flowers
(owners of the flowers on which the plot
stands)
 Twice, stolen from the bees by the
beehive keepers
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Composition
• Honey composition depends on i)
Composition of the nectars where it
originates and ii) external factors.
Carbohydrates
• Carbohydrates makes the largest portion
of the dry matter of honey. It is
responsible for the honey character,
viscosity, hygroscopicity, granulation and
energy values
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•
•
•
•
Monosaccharides and Disaccharides. Of
this fructose predominates but source of
the nectar is important
These account for 85- 95% of honey CHO
Over time, changes in CHO occurs by
enzymatic or acid reversions
After 2 yrs storage at room temperature
Maltose increases at the expense of
dextrose and leavulose
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 Honey
has triglucosylases which
synthesizes these sugars after splitting of
sucrose
 Low water content in honey favors
accumulation of disaccharides but these
are broken to monosaccharide by
invertase
 Monosaccharides like glucose and
fructose remain in solution in presence of
acids
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Acids
• Acids in honey are responsible for its flavor
• The level of acids adds to its stability
towards microorganisms
• Formic acid was the first to be recognized
but others like acetic, butyric, citirc, formic
glucoronic, lactic, maleic, malic are found
• Glucoronic acid is found in amounts that
exceed other acids.
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 Most
of the acids listed above are
intermediates of the Kreb’s cycle. This
indicates biological oxidation usually
found in nectar
 Honey pH ranges between 3.2- 4.5 with a
mean of 3.9. This is determined by
amount of acid present but also amount
of mineral content Ca++, Na+ and K+
 Honey with a high ash content as a high
pH
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Minerals
 Average ash content is 0.17%
 Proteins (Amino Acids)
 Honey contains proteins and their
presence is used to determine
adulteration. Protein constitutes 0.041%
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Enzymes
 Enzymes present include lipases, lactase,
protease, catalase, diastase and invertase
Diastase
 Starch digesting enzyme diastase is used
to determine honey quality
 Diastase is sensitive to heat. Heating
reduces the half life of diastase and
invertase
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Invertase
 Is responsible for changes occurring
during storage of honey
 Bees have been shown to be responsible
for adding invertase to honey. Substrate
for invertase is sucrose which is
hydrolyzed to fructose (Fructoinvertase)
and glucose (glucoinvertase)
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Honey color
 The precursors are unknown. Color of
honey is described as being
polyphenolic and ferric chloride.
Oxidation of these compounds forms
colored compounds
 Color is attributed to: i) combination of
tannates and other polyphenols with iron
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•
•
•
•
ii) Reaction of reducing sugars with
substances containing amino acids –
browning reaction
Iii). Instability of fructose in acid solutions
(caramelization)
Aroma/Flavor
Its mainly from sugars, glucoronic acid
and proline content. Sugars, AA, acids all
contribute to flavor leading to
aroma/flavor characteristic varying
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A compound 5
hydroxymethylfurfuraldehyde shows as the
principle peak in GLC as the one
responsible for satisfactory organoleptically
acceptable honey
Vitamins
• Vitamins are found in negligible amounts
HMF
• Is formed by decomposition of fructose in
the presence of acids
•
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Biological properties of honey
 These vary depending on their plant
origin.
Antibacterial
 Bacteria die in honey. Diluted honey ids
more effective. This is attributed to
presence of inhibines. These rare
sensitive to light and heat. Honey dew
has more antibacterial properties than
floral honey
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One of the inhibines is H2O2 produced by
natural glucose oxidase system in honey
• Thermolability is seen at 80oC for these
inhibines
Pharmacological
• Honey has been used in medicine
throughout time.
• Used as topical application to burns and
wounds. Due to its viscosity it forms a thick
barrier to entry of microbes
•
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It is used to sober drunken patients. Due
to its high fructose content, it speeds up
alcohol metabolism due to catalase
Nutritive Value
• One may survive on honey and milk for 3
months when one starts to show Vit C
deficiency
• Used by invalids and infants because its
more palatable
•
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 One
requires only 100g/day
 John survived in the desert eating wild
honey and locusts
Quality Control of Honey
 Moisture- sugars are responsible for
sweetness sugar content suppresses
fermentation as moisture decreases
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Moisture content varies between 17.2 –
18% with an upper limit of 21%. Viscosity
of honey is due its low moisture content.
• This can be measured using a
refractometer.
Flavor
• Measured using trained panelists. No
instrumentation. Honey should be free
from foreign flavors, aromas associated
with fermentation
•
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Sugar Composition
 Sugar spectrum is as a result of physical
properties of honey. Glucose and
fructose make up to 75% while lower
acceptable limit is 65% for floral and
60% for honeydew.
 Dissacharides (sucrose) upper limit is
5%. Non reducing do not react with
copper reduction methods
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Ageing/heating/adulteration with invert
sugar
 High temperatures (storage above 27 or
heating at 70oC) affect constituents that
are important for flavor and color
 Excessive temperature increases the
production 5HMF from the breakdown of
sugar solution especially those
containing glucose and fructose
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•
•
•
Addition of commercial sugar increases
5HMF which is usually at 10mg/kg. Heating
hydrolysis sugars and 5HMF increases to 30
- 40mg/kg
If 5HMF reaches 150mg/kg the honey has
been adulterated with invert sugars
(sucrose)
Enzyme diastase and invertase are sensitive
to heat. Diastase has a higher tolerance to
temperature and is used to identify honey
that ahs been overheated. Normal honey
has a diastase number 8.
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 Diastase
is measured as amount in mls of
1% starch solution hydrolyzed by enzyme
in 1g honey at 40oC in 1h
 Acids
 Determined by titrable acidity and this
gives history of honey. High acid figure,
honey has been fermented resulting in
alcohol which is converted to acetic acid
by bacteria
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